﻿using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SDKTemplate
{
    /// <summary>  
    /// 获取文件的编码格式  
    /// </summary>  
    public class EncodingType
    {
        /// <summary>  
        /// 给定文件的路径，读取文件的二进制数据，判断文件的编码类型  
        /// </summary>  
        /// <param name="FILE_NAME">文件路径</param>  
        /// <returns>文件的编码类型</returns>  
       

        /// <summary>  
        /// 通过给定的文件流，判断文件的编码类型  
        /// </summary>  
        /// <param name="fs">文件流</param>  
        /// <returns>文件的编码类型</returns>  
        public static System.Text.Encoding GetType(byte[] ss)
        {
            byte[] Unicode = new byte[] { 0xFF, 0xFE, 0x41 };
            byte[] UnicodeBIG = new byte[] { 0xFE, 0xFF, 0x00 };
            byte[] UTF8 = new byte[] { 0xEF, 0xBB, 0xBF }; //带BOM  
            Encoding reVal = Encoding.UTF8;

            
            if (IsUTF8Bytes(ss) || (ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF))
            {
                reVal = Encoding.UTF8;
            }
            else if (ss[0] == 0xFE && ss[1] == 0xFF && ss[2] == 0x00)
            {
                reVal = Encoding.BigEndianUnicode;
            }
            else if (ss[0] == 0xFF && ss[1] == 0xFE && ss[2] == 0x41)
            {
                reVal = Encoding.Unicode;
            }
         
            return reVal;
        }
        /// <summary>  
        /// 判断是否是不带 BOM 的 UTF8 格式  
        /// </summary>  
        /// <param name="data"></param>  
        /// <returns></returns>  
        private static bool IsUTF8Bytes(byte[] data)
        {
            int charByteCounter = 1;　 //计算当前正分析的字符应还有的字节数  
            byte curByte; //当前分析的字节.  
            for (int i = 0; i < data.Length; i++)
            {
                curByte = data[i];
                if (charByteCounter == 1)
                {
                    if (curByte >= 0x80)
                    {
                        //判断当前  
                        while (((curByte <<= 1) & 0x80) != 0)
                        {
                            charByteCounter++;
                        }
                        //标记位首位若为非0 则至少以2个1开始 如:110XXXXX...........1111110X　  
                        if (charByteCounter == 1 || charByteCounter > 6)
                        {
                            return false;
                        }
                    }
                }
                else
                {
                    //若是UTF-8 此时第一位必须为1  
                    if ((curByte & 0xC0) != 0x80)
                    {
                        return false;
                    }
                    charByteCounter--;
                }
            }

            if (charByteCounter > 1)
            {
                throw new Exception("非预期的byte格式");
            }
            return true;
        }
    }
}
